1. Field of the Invention
The invention is directed to a semiconductor wafer comprising a silicon single crystal substrate having a top surface and a stack of layers covering the top surface, and to a method for producing the semiconductor wafer. Specifically, the invention is directed to a layered semiconductor wafer comprising a silicon single crystal substrate having Group III-nitride heteroepitaxial layers deposited thereon.
2. Description of the Related Art
The layered semiconductor wafer is useful as a source for producing electronic and optoelectronic devices, e.g. high-power devices, high-frequency devices like HEMTs (high electron mobility transistors) and light-emitting devices like LEDs (light emitting diodes) and light-detector devices like UV detectors.
There is a considerable crystal lattice mismatch between silicon and Group III-nitrides like e.g. AlN, AlGaN, GaN, and AlInGaN, and a considerable mismatch with regard to coefficients of thermal expansion (CTE). Crystal lattice mismatch and CTE mismatch induce film stress and cause serious problems like poor crystal quality due to formation of dislocations, as well as a deformation by bowing of the layered semiconductor wafer or even cracking of the Group III-nitride layers or the whole layered semiconductor wafer. CTE mismatch produces significant tensile stress after cooling of the layered semiconductor wafer.
Various attempts have been made to reduce film stress. According to US 2009/0008647 A1 crack-free layers can be grown by using e.g. graded AlGaN buffer layers, AlN interlayers, AlN/GaN or AlGaN/GaN-based superlattices, or an in-situ silicon nitride masking step. Although the presence of e.g. an AlGaN buffer layer may provide some compressive stress which counteracts tensile stress caused by CTE mismatch after cooling from the deposition temperature, this counteracting stress is not sufficient for a complete compensation. As a consequence, the deformation of the layered semiconductor wafer after cooling from the deposition temperature remains an issue.
Therefore, it is an object of the claimed invention to provide a proper solution to this problem.